Centrifugal pump impeller

ABSTRACT

An impeller includes an impeller body in which an internal flow path and a recessed section are formed; a lid covering an opening of the recessed section; and a balance weight arranged between the impeller body and the lid. The lid is attached and fixed to the impeller body through an engagement section. Holding sections for the balance weight are formed in a back-side surface of the lid. When attaching and fixing the lid to the impeller body, the balance weight is sandwiched between the holding section of the lid and the impeller body to be fixed.

TECHNICAL FIELD

A technique disclosed herein relates to a centrifugal pump impeller.

BACKGROUND ART

Conventionally, a centrifugal pump has been used for delivering, e.g.,drainage. Among various impellers attached to the centrifugal pump, anon-clog impeller in which a flow path connecting between an inletopening through a first end surface and an outlet opening through acircumferential surface is formed has been known as an impeller in whichit is less likely to cause clogging of, e.g., drainage containing solidsubstances such as impurities (see, e.g., Patent Document 1).

The non-clog impeller has a single vane, and therefore is formed innon-symmetric shape about a rotation axis. Thus, a part of the impellerdisclosed in Patent Document 1 is removed in order to achieve staticbalance at rest and dynamic balance during rotation in air (hereinaftercollectively referred to as “mechanical balance”). In a second endsurface of the substantially cylindrical impeller, which is on anopposite side to the first end surface in which the inlet is formed,such removal allows formation of a recessed section which opens throughthe second end surface, and which is recessed in a cylindrical axisdirection in the second end surface. As in the foregoing impeller, in animpeller made of synthetic resin, a recessed section which opens througha second end surface, and which is recessed in a cylindrical axisdirection in the second end surface may be formed in order to reduce orprevent shrinkage caused when forming the impeller due to thesubstantially constant thickness of the impeller.

However, the opening of the recessed section is exposed, resulting in apower loss due to fluid turbulence. Thus, in the impeller disclosed inPatent Document 1, a lid is attached to the second end surface, and theopening of the recessed section is covered by the lid. Consequently, theflat second end surface of the impeller is defined.

CITATION LIST Patent Document

PATENT DOCUMENT 1: Japanese Patent Publication No. 2006-291937

SUMMARY OF THE INVENTION Technical Problem

In the conventional impeller disclosed in Patent Document 1, the lid isfixed to an impeller body with bolts. Thus, its assembly process iscomplicated. In addition, in the impeller disclosed in Patent Document1, a balance weight is attached to a back-side surface of the lid withthe bolts in order to achieve the mechanical balance and balance duringrotating the impeller in water (hydraulic balance). Thus, there is adisadvantage that not only a lid attachment process but also a balanceweight attachment process are separately required.

The centrifugal pump impeller disclosed herein is an advantageousimpeller for simplifying an attachment structure of a lid attached to animpeller body, and simplifying an assembly process.

Solution To the Problem

Inventors of the present invention have focused on an engagementstructure between an impeller body and a lid; and have arrived at aconfiguration in which an engagement between the impeller body and thelid is facilitated through an engagement section, and a balance weightis sandwiched between the lid engaged with the impeller body and theimpeller body to fix the balance weight to the impeller body.

An example of a centrifugal pump impeller includes an impeller bodyhaving a substantially cylindrical shape with first and second endsurfaces facing each other in a cylindrical axis direction, and with acircumferential surface interposed between the first and second endsurfaces; and including an internal flow path which connects between aninlet opening in the first end surface and an outlet opening in thecircumferential surface, and a recessed section which opens in thesecond end surface, and which is recessed in the cylindrical axisdirection in the second end surface; a lid which is attached to thesecond end surface of the impeller body, and which covers the opening ofthe recessed section so that the second end surface of the impeller bodydefines a flat surface; and a balance weight arranged between theimpeller body and the lid. The lid is attached and fixed to the impellerbody through an engagement section, and holding sections of the balanceweight are formed in a back-side surface. When the lid is attached andfixed to the impeller body, the balance weight is sandwiched between theholding section of the lid and the impeller body, and is fixed by theholding section of the lid and the impeller body.

Advantages of the Invention

According to the foregoing configuration, the lid is attached and fixedto the impeller body through the engagement section. By attaching andfixing the lid to the impeller body, the balance weight is sandwichedbetween the holding section of the lid and the impeller body, and thenthe balance weight is attached and fixed to the impeller body. That is,the lid and the balance weight are simultaneously attached to theimpeller body, thereby simplifying an assembly process of the impeller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a submersible pump including acentrifugal pump impeller which is illustrated as an example.

FIG. 2 is a perspective view of the impeller.

FIG. 3 is a front view of the impeller.

FIG. 4 is a bottom view of the impeller.

FIG. 5 is a V-V cross-sectional view of FIG. 4.

FIG. 6 is a plan view of an impeller body in a state in which a lid isremoved.

FIG. 7 is a view illustrating a back-side surface of the lid.

FIG. 8 is a VIII-VIII cross-sectional view of FIG. 7.

FIG. 9 is an enlarged plan view around a boss section of the impellerbody.

FIG. 10 is an enlarged cross-sectional view around the boss section ofthe impeller body.

FIG. 11 is a perspective view of an upper balance weight.

FIG. 12 is a perspective view of a lower balance weight.

DESCRIPTION OF EMBODIMENTS

An example of a centrifugal pump impeller includes an impeller bodyhaving a substantially cylindrical shape with first and second endsurfaces facing each other in a cylindrical axis direction, and with acircumferential surface interposed between the first and second endsurfaces; and including an internal flow path which connects between aninlet opening in the first end surface and an outlet opening in thecircumferential surface, and a recessed section which opens in thesecond end surface, and which is recessed in the cylindrical axisdirection in the second end surface; a lid which is attached to thesecond end surface of the impeller body, and which covers the opening ofthe recessed section so that the second end surface of the impeller bodydefines a flat surface; and a balance weight arranged between theimpeller body and the lid. The lid is attached and fixed to the impellerbody through an engagement section, and holding sections of the balanceweight are formed in a back-side surface. When the lid is attached andfixed to the impeller body, the balance weight is sandwiched between theholding section of the lid and the impeller body, and is fixed by theholding section of the lid and the impeller body.

The lid is attached and fixed to the impeller body through theengagement section, thereby sandwiching the balance weight between theholding section of the lid and the impeller body. Consequently, thebalance weight is attached and fixed to the impeller body. As describedabove, the lid and the balance weight are simultaneously attached to theimpeller body, thereby facilitating an assembly process of the impeller.

The engagement section may include engagement grooves formed in theimpeller body or the lid; and engagement claws which are formed in thelid or the impeller body, and which are engaged with the engagementgrooves by elastically deforming when attaching the lid to the impellerbody.

The engagement groove and the engagement claw can be engaged with eachother without using, e.g., tools. Thus, the tools etc. are not requiredwhen attaching the lid to the impeller body, thereby further simplifyingthe assembly process of the impeller.

A plurality of pins may be formed so as to protrude from the back-sidesurface of the lid; and a plurality of pinholes into which the pins arefitted may be formed so as to open through the second end surface of theimpeller body.

Positions of the pin and the pinhole are adjusted to each other, and theposition of the lid is determined on the impeller body. In combinationwith the engagement in the engagement section, the fitting of the pininto the pinhole allows the lid to be more firmly fixed to the impellerbody.

Each of the pinholes may be formed in a boss section provided in thesecond end surface of the impeller body. A plurality of protrusions maybe formed with spacing in a circumferential direction in acircumferential surface of the boss section. Fitting holes which have alarger diameter than that of the boss section, and which have a smallerdiameter than that of a circle defined by connecting tip ends of theplurality of protrusions may be formed in the balance weight; and, inorder to fix the balance weight to the impeller body, the fitting holesof the balance weight may be fitted onto the boss sections with theprotrusions being pressed against the boss sections. The holding sectionof the lid is formed in circular shape so as to surround the pin, andholds the balance weight in a section around the fitting hole.

The fitting hole of the balance weight is fitted onto the boss sectionof the impeller body, and therefore the balance weight can be correctlypositioned on a predetermined section of the impeller body. In addition,the fitting hole of the balance weight is fitted onto the boss sectionof the impeller body, and the holding section of the lid presses againstthe section around the fitting hole. This reduces or prevents occurrenceof rattling of the balance weight, and firmly fixes the balance weightto the impeller body.

A plurality of reinforcement ribs extending in a radial direction may beformed inside the recessed section of the impeller body, and an endsurface of the reinforcement rib in the cylindrical axis direction maybe a mounting surface on which the balance weight is mounted. The bosssection may be integrally formed with the reinforcement rib in themounting surface of the reinforcement rib.

The reinforcement rib improves a strength of the impeller body. Inaddition, the boss section is integrally formed with the reinforcementrib, thereby improving stiffness of the boss section. The balance weightis more stably fixed to the impeller body.

An embodiment of the impeller will be described below with reference tothe drawings. Note that the embodiment below has been set forth merelyfor purposes of a preferred example in nature. FIG. 1 illustrates asubmersible pump 1 including an impeller which is illustrated as anexample. The submersible pump 1 includes a pump section 21 with animpeller 6, and a motor section 22 with a motor 3 for driving theimpeller 6. In the submersible pump 1, the pump section 21 is arrangedbelow an oil casing 23, and the motor section 22 is arranged above theoil casing 23. That is, the pump section 21 and the motor section 22 arearranged one above the other. The submersible pump 1 is a lightweightpump in which a head cover 34 and a pump casing 4 which will bedescribed later are made of predetermined resin material.

The motor section 22 includes the motor 3 with a stator 31 and a rotor32; a stator casing 33 covering the stator 31 of the motor 3; and thehead cover 34 attached to an upper end of the stator casing 33. Arotating shaft 35 of the motor 3 vertically extends.

The stator casing 33 is formed in substantially cylindrical shape withupper and lower openings. The upper opening of the stator casing 33 isclosed with a motor cover 36, and a bearing 35 a rotatably supporting anupper end section of the rotating shaft 35 is provided on a lowersurface of the motor cover 36.

The head cover 34 is attached to the upper end of the stator casing 33.The head cover 34 has an upper wall and a circumferential wall whichdownwardly extends from a circumferential section of the upper wall, andwhich is fixed to an upper end section of the stator casing 33. Inaddition, the head cover 34 has an inverted U-shaped cross section.Thus, the head cover 34 and the motor cover 36 defines a housing space34 a in which various electric components are housed. A cable boot intowhich a power feeding cable for feeding power to the motor 3 is insertedis attached so as to pass through the upper wall of the head cover 34,and a handle 34 b is attached to a center section of an upper surface ofthe upper wall. The head cover 34 is fixed to the oil casing 23 with aplurality of bolts 37 (only one bolt is illustrated in the figure)arranged at predetermined interval in the circumferential direction.That is, the bolt 37 inserted into a through-hole formed in acircumferential section of the head cover 34 passes through the motorcover 36. Then, the bolt 37 downwardly extends along an innercircumferential surface of the stator casing 33, and is screwed into acircumferential section of the oil casing 23. In such a manner, in thesubmersible pump 1, the long vertically-extending bolt 37 fixes the headcover 34, the stator casing 33, and the motor cover 36 to the oil casing23 at one time. Such a configuration allows reduction in the number ofcomponents and the number of assembly steps of the submersible pump 1.

The oil casing 23 is attached to a lower end of the stator casing 33,and the lower opening of the stator casing 33 is closed with the oilcasing 23. The pump casing 4 is attached to a lower side of the oilcasing 23, and therefore the oil casing 23 and the pump casing 4 definean oil chamber 53 filled with lubricating oil. A through-hole into whichthe rotating shaft 35 of the motor 3 is inserted is formed in the oilcasing 23, and a bearing 35 b rotatably supporting a middle section ofthe rotating shaft 35 is attached to an upper surface of the oil casing23. In the oil chamber 53 defined by the oil casing 23 and the pumpcasing 4, the rotating shaft 35 is sealed by a mechanical seal 51, and acircular wall 52 is provided, which surround a substantially entireouter circumferential section of the mechanical seal 51.

The pump section 21 includes the impeller 6 attached to a lower end ofthe rotating shaft 35 of the motor 3, and the pump casing 4. Thesubmersible pump 1 is a centrifugal pump. A first pump casing 41 on anupper side, which defines the oil chamber 53 together with the oilcasing 23, and a second pump casing 42 on a lower side are integrated bywelding, thereby forming the pump casing 4. The first pump casing 41 andthe second pump casing 42 are integrated by welding as described above,and therefore a flange is not required, which is required, e.g., whenintegrating two pump casings with a bolt-nut fastening means.Consequently, the size of the submersible pump 1 is reduced.

A through-hole into which the rotating shaft 35 is inserted is formed inan upper section of the pump casing 4, and a volute chamber 43 in whichthe impeller 6 is housed is formed inside the pump casing 4. The pumpcasing 4 has a lower opening, and a liner ring 44 with an opening 44 a,which supports a wear ring section 692 which is a lower end section ofthe impeller 6 is attached to such an opening. A discharge section 45which laterally protrudes, and which is upwardly curved is integrallyformed with a side section of the pump casing 4. The discharge section45 communicates with the volute chamber 43, and has a discharge port 45a with an upper opening. The discharge port 45 a is connected to anoutlet pipe which is not shown in the figure. Four downwardly-extendinglegs 46 (only three legs 46 are illustrated in FIG. 1) are arranged in alower section of the pump casing 4 in a predetermined pattern, and lowerends of the legs 46 are attached and fixed to a seat 7. The seat 7includes a body section 71 made of synthetic resin; and a cover 72 whichcovers a lower side of the body section 71, and which is made of rubber.Inserting sections 73 into which the lower ends of the legs 46 areinserted, and in which the lower ends of the legs 46 are fastened withscrews are integrally formed with the body section 71 so as to upwardlyprotrude. A damping rubber member or damping steel plate 74 isinterposed between a lower surface of the leg 46 and the insertingsection 73. The seat 7 functions to reduce or prevent displacement of aposition where the submersible pump 1 is arranged due to the cover 72,and to control vibration by the damping rubber member or damping steelplate 74 when driving the submersible pump 1.

As illustrated in FIGS. 2-5, the impeller 6 is a non-clog impellerhaving a substantially cylindrical shape, and is fixed to the lower endof the rotating shaft 35 so that a cylindrical axis of the impeller 6 iscoaxial to the rotating shaft 35 (see FIG. 1). The impeller 6 includesan impeller body 61, and a lid 62 attached to an upper end surface ofthe impeller body 61. In addition, in order to achieve mechanical andhydraulic balance, the impeller 6 also includes an upper balance weight63 and a lower balance weight 64. Although details will be describedlater, the upper balance weight 63 is arranged and fixed between theimpeller body 61 and the lid 62, and the lower balance weight 64 isembedded in the wear ring section 692 of the impeller body 61 asillustrated in FIG. 5.

The impeller body 61 has a substantially cylindrical shape. An inlet 601opening at the bottom of the impeller body 61 is formed in a lower endsurface of the impeller body 61, and an outlet 602 opening through aside of the impeller body 61 is formed in a predetermined section of acircumferential surface of the impeller body 61. An internal flow path603 extending in the cylindrical axis direction is formed inside theimpeller 6, and the internal flow path 603 connects between the inlet601 and the outlet 602. An external flow path 604 inwardly recessed inthe radial direction is formed in an outer circumferential surface ofthe impeller body 61. The external flow path 604 is not a flow pathextending in the cylindrical axis direction, and the center of the flowpath is positioned on a plane perpendicular to the cylindrical axis ofthe impeller body 61. The external flow path 604 reaches a downstreamside of the internal flow path 603 at the outlet 602, and extends acrossa substantially entire perimeter of the impeller 6. The external flowpath 604 is defined by a vane 605. The vane 605 is a so-called “singleradial-flow vane (centrifugal vane), and the centrifugal vane 605increases the pressure of water in the external flow path 604, and thendischarges such water to an outer circumferential side (outer side inthe radial direction). A first flange section 681 outwardly protrudingin the radial direction around an entire circumference is formed abovethe external flow path 604 of the impeller body 61. In addition, asecond flange section 682 outwardly protruding in the radial directionaround the entire circumference is also formed below the external flowpath 604. The second flange section 682 horizontally divides theimpeller 6 into a lower section where the inlet 601 is formed, and anupper section where the outlet 602 is formed. That is, the impeller 6 isa closed-type impeller in which the second flange section 682 dividesbetween the inlet 601 and the outlet 602.

A shaft support section 691 is formed so as to upwardly protrude in thecenter of the upper end surface of the impeller body 61, which is abovethe first flange section 681. The shaft support section 691 is made ofpredetermined metal material, and is provided with an attachment holeinto which the rotating shaft 35 of the motor 3 is inserted to be fixed.In addition, the downwardly-protruding wear ring section 692 insertedinto the opening 44 a of the pump casing 4 is formed below the secondflange section 682 of the impeller body 61.

In order to reduce power of the submersible pump 1, the first and secondflange sections 681 and 682 are set to a smaller diameter so that thediameter of the impeller body 61 becomes as small as possible. Thus, asillustrated in FIGS. 3 and 5, the impeller body 61 is designed withalmost no step between the second flange section 682 and the wear ringsection 692. The diameters of the first and second flange sections 681and 682 may be further reduced in order to, e.g., eliminate such a step.Conversely, the diameter of the wear ring section 692 is increased sothat the diameter of the inlet 601 is increased, thereby eliminating thestep between the second flange section 682 and the wear ring section692.

The impeller body 61 is made of synthetic resin. As illustrated in FIGS.5 and 6, a recessed section 611 recessed in the cylindrical axisdirection in the upper end surface of the impeller body 61 is formed inorder to reduce or prevent shrinkage caused when forming the impellerdue to the substantially constant thickness of the impeller. Asillustrated in FIG. 6, the recessed section 611 extends substantiallythree-fourths of the entire perimeter from an opening side of the outlet602 (upper side as viewed in FIG. 6), in the counterclockwise andcircumferential directions. In addition, as illustrated in FIG. 5, therecessed section 611 is formed so that the depth is relatively shallowon the opening side of the outlet 602 (right side as viewed in FIG. 5),and the depth is relatively deep on a side opposite to the opening sideof the outlet 602 (left side as viewed in FIG. 5).

Reinforcement ribs 612 extending in the radial direction, and connectingbetween the shaft support section 691 and a circumferential section ofthe impeller body 61 are formed in an upper end section of the impellerbody 61. In the present embodiment, in the impeller body 61 illustratedin FIG. 6, three reinforcement ribs 612 are formed at predeterminedangles in an upper half region corresponding to the opening side of theoutlet 602, and a single reinforcement rib 612 is formed in a lower halfregion corresponding to the side opposite to the opening side of theoutlet 602. Three of the four reinforcement ribs 612 are arranged insidethe recessed section 611. As illustrated in, e.g., FIG. 10, the threereinforcement ribs 612 arranged on the opening side of the outlet 602are also used as a mounting section on which the upper balance weight 63is mounted. That is, an upper end surface of each of the reinforcementribs 612 serves as a mounting surface 614 on which the upper balanceweight 63 is mounted. Further, a boss section 613 for fixing the upperbalance weight 63 is formed in the substantially center of thereinforcement rib 612 in the radial direction.

As illustrated in FIGS. 9 and 10, the boss section 613 is formed incircular shape as viewed in plan, which has a diameter larger than thewidth of the reinforcement rib 612. An upwardly-opening pinhole 615which extends in the cylindrical axis direction is formed in the centerof the boss section 613. In an outer circumferential surface of the bosssection 613, three protrusions 616 outwardly protruding in the radialdirection are integrally formed with the boss section 613 at equalinterval in the circumferential direction.

As illustrated in FIG. 11, the upper balance weight 63 made ofpredetermined metal material is formed in substantially fan-like shapeby cutting a section corresponding to a predetermined angular range froman annular disk-like member having a predetermined thickness. The upperbalance weight 63 has a flattened shape in which the width of the upperbalance weight 63 in the radial direction is larger than the thicknessof the upper balance weight 63 in the cylindrical axis direction(vertical direction). As illustrated in FIG. 6, the upper balance weight63 is arranged between the shaft support section 691 and thecircumferential section of the impeller body 61. Thus, the innerdiameter of the upper balance weight 63 is set so as to be larger thanthe diameter of the shaft support section 691, and the outer diameter ofthe upper balance weight 63 is set so as to be smaller than the diameterof the circumferential section of the impeller body 61. The shape of theupper balance weight 63 is not limited, and may be suitably set so thata required weight can be ensured under a condition where the upperbalance weight 63 is arranged between the impeller body 61 and the lid62. In the upper balance weight 63, three holes 631 passing through theupper balance weight 63 in a thickness direction are formedcorresponding to the three boss sections 613. Each of such holes is afitting hole 631 fitted onto the boss section 613. As hypotheticallyillustrated in FIG. 9, the diameter of such a hole is set so as to belarger than that of the boss section 613, and to be smaller than that ofa circle defined by connecting tip ends of the protrusions 616.

As illustrated in enlarged views of FIGS. 9 and 10, the upper balanceweight 63 is mounted on the mounting surface 614 of the reinforcementrib 612 so that each of the fitting holes 631 is fitted onto the bosssection 613. Thus, the upper balance weight 63 is positioned in apredetermined section of the upper end surface of the impeller body 61on the opening side of the outlet 602. The fitting hole 631 of the upperbalance weight 63 is set so as to have the diameter larger than that ofthe boss section 613, and smaller than that of the circle defined byconnecting the tip ends of the protrusions 616. Thus, a part of theprotrusions 616 is pressed against the boss section 613, thereby fittingthe fitting hole onto the boss section 613. This reduces the rattling ofthe upper balance weight 63.

As illustrated in FIGS. 7 and 8, the lid 62 has a circular disk-likeshape, and a through-hole 621 into which the shaft support section 691of the impeller body 61 is inserted is formed in the center of the lid62. The lid 62 is made of synthetic rein. A front-side surface of thelid 62 is flat. On each of a side corresponding to the opening of theoutlet 602 and its opposite side with respect to the cylindrical axis inthe circumferential section of the lid 62, two engagement claws 622 areintegrally formed with the lid 62 at predetermined interval in thecircumferential direction. The engagement claw 622 is a claw to beengaged with an engagement groove 683 formed at a circumference of theupper end section of the impeller body 61, and the engagement claw 622and the engagement groove 683 serve as an engagement means for attachingand fixing the lid 62 to the impeller body 61.

In positions of a back-side surface of the lid 62 corresponding to theboss sections 613 of the impeller body 61, three pins 623 are formed soas to protrude from the back-side surface. As illustrated in FIG. 10,when attaching the lid 62 to the impeller body 61, each of the pins 623is fitted into the pinhole 615 formed in the boss section 613. Inaddition to the engagement of the engagement claw 622 with theengagement groove 683, the fitting of the pin 623 into the pinhole 615allows the lid 62 to be more stably attached and fixed to the impellerbody 61. Holding sections 624 for holding the upper balance weight 63are further formed so as to protrude from the back-side surface of thelid 62. The holding section 624 is formed in circular shape so as tosurround the pin 623. As illustrated in FIG. 10, when attaching andfixing the lid 62 to the impeller body 61, a lower surface of theholding section 624 downwardly presses against an upper surface of theupper balance weight 63 around the boss section 613. Thus, the upperbalance weight 63 is sandwiched between the lid 62 and the impeller body61.

In the lid 62, two through-holes 625 are formed on each of the openingside of the outlet 602 and its opposite side. Such through-holes are airvent holes 625 through which air is vented from the recessed section 611of the impeller body 61 to fill the recessed section 611 with water. Airvent holes may be formed in the upper balance weight 63. In such a case,such air vent holes are desirably formed in the same positions as thoseof the air vent holes 625 formed in the lid 62. The air vent holes 625are provided in the lid 62 to fill the recessed section 611 with wateras described above. Thus, this reduces or prevents a loss of mechanicalbalance of the impeller 6 due to remaining air in the recessed section611, and reduces occurrence of vibration when driving the impeller 6.

As illustrated in FIGS. 3 and 4, the lower balance weight 64 is embeddedin the wear ring section 692 on the opening side of the outlet 602 ofthe impeller body 61. As illustrated in, e.g., FIG. 12, the lowerbalance weight 64 made of predetermined metal material is a plate curvedin arc, and has a vertically-elongated shape in which a height in thecylindrical axis direction is larger than a thickness in the radialdirection. As illustrated in FIG. 4, the lower balance weight 64 isembedded in the wear ring section 692 so that a lower end surface of thelower balance weight 64 is exposed in the lower end surface of theimpeller body 61. Two through-holes 641 are formed in predeterminedpositions of the lower balance weight 64, and each through-hole 641serves as a positioning hole into which a positioning pin 8 of a mold isinserted. A notch 642 is formed in a center section of a lower end ofthe lower balance weight 64. When forming the impeller body 61 bymolding, a section corresponding to the notch 642 is filled with resin,and therefore a retaining section 694 is formed, which crosses the lowerbalance weight 64 in the thickness direction as illustrated in FIG. 4.

Next, a manufacturing process of the impeller body 61 will be brieflydescribed. First, the shaft support section 691 and the lower balanceweight 64 are arranged in predetermined positions inside the mold (notshown in the figure). In such a state, a position of the lower balanceweight 64 in the circumferential direction, and an inclination of thelower balance weight 64 are determined by the two positioning pins 8 asillustrated in FIG. 12. The positioning pin 8 includes a small-diametersection 81 on a tip end side, and a large-diameter section 82 on a baseend side. A position of the lower balance weight 64 in the radialdirection is also determined by a position of a step defined by suchsections having the different diameters. In such a manner, the lowerbalance weight 64 can be accurately positioned in a predeterminedsection inside the mold, thereby ensuring the lower balance weight 64embedded in the thin wear ring section 692 of the impeller body 61.

Then, the impeller body 61 is formed by a well-known resin molding. Asillustrated in FIGS. 2 and 3, holes 693 are formed in the wear ringsection 692 of the molded impeller body 61 by the positioning pins 8.

Next, the separately-prepared upper balance weight 63 is attached to theupper end surface of the molded impeller body 61. As described above, inthe upper balance weight 63, the fitting hole 631 of the upper balanceweight 63 is fitted onto the boss section 613 with the protrusions 616of the boss section 613 being pressed against the fitting hole 631.

Subsequently, the separately-molded lid 62 is attached to the impellerbody 61. In such a state, the pin 623 of the lid 62 is fitted into thepinhole 615 of the impeller body 61, and the engagement claw 622 of thelid 62 is elastically deformed to be engaged with the engagement groove683 of the impeller body 61. When attaching and fixing the lid 62 to theimpeller body 61, the holding sections 624 of the lid 62 press againstthe upper balance weight 63. Thus, attachment of the upper balanceweight 63 to the impeller body 61 is completed.

As described above, in the impeller 6 having the foregoingconfiguration, the fastening means such as bolts is not used to fix thelid 62 to the impeller body 61, and the engagement claws 622 are engagedwith the engagement grooves 683 to attach and fix the lid 62 to theimpeller body 61. Thus, tools etc. are not required for the assemblyprocess, and the assembly of the impeller 6 is simplified. In addition,when attaching the lid 62 to the impeller body 61, the upper balanceweight 63 is fixed to the impeller body 61. Consequently, the assemblyprocess of the impeller 6 is further facilitated.

The engagement claws 622 are provided in the lid 62, and the engagementgrooves 683 opening toward outside are provided in the circumferentialsection of the impeller body 61. Thus, in a state in which the lid 62 isattached to the impeller body 61, the engagement sections are notprotrude from the front-side surface of the lid 62, thereby ensuring theflat surface at the upper end of the impeller 6. This is advantageous toreduce a power loss. Note that engagement grooves may be provided in thelid 62, and engagement claws may be provided in the impeller body 61.The engagement section where the lid 62 is engaged with the impellerbody 61 is not limited to the combination of the engagement claw 622 andthe engagement groove 683, and any configuration may be employed.

The circumferential section of the lid 62 is fixed to the impeller body61 by the engagement claws 622 and the engagement grooves 683, and thepins 623 provided in the lid 62 are fitted into the pinholes 615 of theimpeller body 61. Thus, an inner section of the lid 62 in the radialdirection can be fixed to the impeller body 61. Consequently, the innersection of the lid 62 in the radial direction is not apart from theimpeller body 61.

The fitting hole 631 of the upper balance weight 63 is fitted onto theboss section 613 of the impeller body 61. Thus, the upper balance weight63 can be correctly positioned on the predetermined section of theimpeller body 61, and the occurrence of the rattling of the upperbalance weight 63 can be reduced or prevented.

The reinforcement rib 612 improves the strength of the impeller body 61itself. In addition, the upper balance weight 63 and the boss section613 used for the fixing of the lid are integrally formed with thereinforcement rib 612, thereby improving the stiffness of the bosssection 613. This is advantageous to more stably fix the upper balanceweight 63 and the lid 62 to the impeller body 61.

Unlike the upper balance weight 63, the lower balance weight 64 has thevertically-elongated shape, thereby embedding the lower balance weight64 in the wear ring section 692 which is thin in the radial direction.The lower balance weight 64 is embedded in the impeller body 61, andtherefore it is not necessary to attach the balance weight to the secondflange section 682. This allows the diameter of the inlet 601 of theimpeller 6 to be as large as possible, thereby ensuring predeterminedsubstance passage properties. In addition, the diameters of the firstand second flange sections 681 and 682 become as small as possible inorder to reduce the diameter of the impeller 6, thereby reducing thepower of the submersible pump 1.

The lower end surface of the lower balance weight 64 embedded in thewear ring section 692 is exposed in the lower end surface of theimpeller body 61, and therefore there is a possibility that the lowerbalance weight 64 is disengaged during use of the impeller 6. However,the retaining section 694 is configured by forming the notch 642 at thelower end of the lower balance weight 64, thereby reducing or preventingthe disengagement of the lower balance weight 64. In the presentembodiment, the retaining section 694 is configured by forming the notch642 at the lower end of the lower balance weight 64. However, athrough-hole passing through the lower balance weight 64 in thethickness direction may be formed in, e.g., a middle section of thelower balance weight 64 in the height direction, thereby forming a resinretaining section crossing the lower balance weight 64 in the thicknessdirection. Alternatively, the entire lower balance weight 64 may beembedded in the impeller body 61, and therefore the lower end of thelower balance weight 64 may not be exposed. In such a case, theretaining section is not required.

In the foregoing embodiment, the lower balance weight 64 is embedded inthe wear ring section 692. However, e.g., if the height of the lowerbalance weight 64 is increased under a condition where the requiredweight is ensured, an upper end section of the lower balance weight 64may be positioned corresponding to the second flange section 682.

The lower balance weight 64 is not limited to the configuration in whichthe lower balance weight 64 is embedded in the wear ring section 692,and the lower balance weight 64 may be embedded in any parts of thecircumferential section of the impeller body 61.

The impeller is not limited to the impeller made of synthetic resin.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 Submersible Pump-   6 Impeller-   601 Inlet-   602 Outlet-   603 Internal Flow Path-   61 Impeller Body-   611 Recessed Section-   612 Reinforcement Rib-   613 Boss Section-   615 Pinhole-   616 Protrusion-   62 Lid-   622 Engagement Claw-   623 Pin-   624 Holding Section-   63 Upper Balance Weight-   631 Fitting Hole-   683 Engagement Groove

1. A centrifugal pump impeller, comprising: an impeller body having asubstantially cylindrical shape with first and second end surfacesfacing each other in a cylindrical axis direction, and with acircumferential surface interposed between the first and second endsurfaces; and including an internal flow path which connects between aninlet opening in the first end surface and an outlet opening in thecircumferential surface, and a recessed section which opens in thesecond end surface, and which is recessed in the cylindrical axisdirection in the second end surface; a lid which is attached to thesecond end surface of the impeller body, and which covers the opening ofthe recessed section so that the second end surface of the impeller bodydefines a flat surface; and a balance weight arranged between theimpeller body and the lid, wherein the lid is attached and fixed to theimpeller body through an engagement section, and holding sections of thebalance weight are formed in a back-side surface; and, when the lid isattached and fixed to the impeller body, the balance weight issandwiched between the holding section of the lid and the impeller body,and is fixed by the holding section of the lid and the impeller body. 2.The centrifugal pump impeller of claim 1, wherein the engagement sectionincludes engagement grooves formed in the impeller body or the lid; andengagement claws which are formed in the lid or the impeller body, andwhich are engaged with the engagement grooves by elastically deformingwhen attaching the lid to the impeller body.
 3. The centrifugal pumpimpeller of claim 1, wherein a plurality of pins are formed so as toprotrude from the back-side surface of the lid; and a plurality ofpinholes into which the pins are fitted are formed so as to open in thesecond end surface of the impeller body.
 4. The centrifugal pumpimpeller of claim 3, wherein each of the pinholes is formed in a bosssection provided in the second end surface of the impeller body; aplurality of protrusions are formed with spacing in a circumferentialdirection in a circumferential surface of the boss section; fittingholes which have a larger diameter than that of the boss section, andwhich have a smaller diameter than that of a circle defined byconnecting tip ends of the plurality of protrusions are formed in thebalance weight, and, in order to fix the balance weight to the impellerbody, the fitting holes of the balance weight are fitted onto the bosssections with the protrusions being pressed against the boss sections;and the holding section of the lid is formed in circular shape so as tosurround the pin, and holds the balance weight in a section around thefitting hole.
 5. The centrifugal pump impeller of claim 4, wherein aplurality of reinforcement ribs extending in a radial direction areformed inside the recessed section of the impeller body, and an endsurface of the reinforcement rib in the cylindrical axis direction is amounting surface on which the balance weight is mounted; and the bosssection is integrally formed with the reinforcement rib in the mountingsurface of the reinforcement rib.